Stephenville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stephenville clear sky chart from 2005-11-06 to 2024-01-22.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	24% 13% 5% 9% 7% 3 4 4 4 5% 21%	74624
	Night	24% 15% 6% 11% 8% 3 4 3 4 5% 17%	75306
Transparency	Day	67% 4 12% 13% 4	74327
	Night	71% 4 10% 11% 4	75138
Seeing	Day	32% 15% 26% 18% 8% 2	16757
	Night	31% 14% 24% 23% 8% 1	23995

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 22% 10% 21% 12% 4 3 2 2 2 4	1516
	11th to 20th	Day	18% 22% 9% 18% 13% 5% 3 2 3 2 4	1520
	21st to end	Day	15% 18% 10% 24% 16% 4 3 2 2 2 5%	1593
February	1st to 10th	Day	19% 15% 7% 20% 17% 6% 3 3 3 2 5%	1485
	11th to 20th	Day	18% 17% 8% 15% 15% 4 4 4 3 2 11%	1613
	21st to end	Day	13% 15% 7% 16% 15% 7% 5% 2 4 4 12%	1480
March	1st to 10th	Day	16% 14% 6% 14% 11% 6% 5% 4 4 5% 15%	1796
	11th to 20th	Day	20% 16% 8% 13% 8% 4 6% 4 4 4 15%	1855
	21st to end	Day	17% 16% 7% 12% 9% 4 3 4 4 4 20%	2376
April	1st to 10th	Day	24% 17% 8% 11% 6% 3 4 3 3 5% 16%	2160
	11th to 20th	Day	20% 12% 4 8% 4 3 4 4 5% 7% 29%	2160
	21st to end	Day	26% 10% 5% 5% 5% 2 5% 3 4 4 30%	2394
May	1st to 10th	Day	26% 11% 4 6% 3 3 3 4 4 6% 30%	2520
	11th to 20th	Day	22% 11% 3 5% 4 3 4 3 4 6% 35%	2478
	21st to end	Day	28% 8% 3 5% 5% 3 5% 4 5% 7% 28%	2724
June	1st to 10th	Day	29% 8% 3 6% 5% 3 4 5% 5% 7% 24%	2662
	11th to 20th	Day	23% 6% 3 6% 4 2 4 5% 6% 8% 33%	2700
	21st to end	Day	30% 10% 3 6% 5% 3 4 4 4 6% 26%	2684
July	1st to 10th	Day	24% 8% 3 5% 5% 3 5% 5% 6% 7% 30%	2520
	11th to 20th	Day	25% 8% 3 5% 5% 3 4 4 5% 6% 32%	2520
	21st to end	Day	28% 9% 4 6% 5% 3 4 4 5% 6% 28%	2745
August	1st to 10th	Day	23% 7% 3 6% 6% 3 4 6% 6% 8% 29%	2506
	11th to 20th	Day	26% 7% 3 6% 5% 3 4 4 6% 6% 29%	2433
	21st to end	Day	24% 7% 3 5% 6% 3 4 5% 5% 9% 29%	2386
September	1st to 10th	Day	24% 7% 3 6% 6% 3 4 4 6% 7% 30%	2160
	11th to 20th	Day	29% 9% 3 6% 6% 2 4 4 5% 6% 25%	2089
	21st to end	Day	29% 10% 3 7% 5% 3 3 5% 5% 6% 24%	1980
October	1st to 10th	Day	25% 11% 3 6% 4 2 4 5% 5% 7% 28%	1843
	11th to 20th	Day	29% 13% 5% 7% 5% 4 3 3 4 7% 20%	1714
	21st to end	Day	28% 19% 5% 9% 5% 2 4 4 4 5% 16%	1782
November	1st to 10th	Day	31% 21% 5% 8% 6% 3 5% 3 4 4 10%	1670
	11th to 20th	Day	27% 22% 7% 9% 5% 3 4 3 3 4 13%	1525
	21st to end	Day	23% 25% 11% 12% 6% 3 4 4 3 3 6%	1436
December	1st to 10th	Day	24% 24% 10% 15% 7% 3 3 3 2 2 6%	1330
	11th to 20th	Day	30% 18% 9% 17% 8% 3 3 3 2 2 5%	1668
	21st to end	Day	23% 21% 11% 17% 8% 2 3 2 3 4 6%	2601
January	1st to 10th	Night	20% 22% 11% 18% 12% 4 3 2 2 2 4	2649
	11th to 20th	Night	19% 21% 9% 18% 12% 6% 4 2 2 2 4	2660
	21st to end	Night	16% 16% 9% 23% 15% 5% 4 3 2 2 5%	2797
February	1st to 10th	Night	17% 16% 7% 22% 19% 7% 3 2 1 2 4	2471
	11th to 20th	Night	17% 15% 9% 17% 14% 5% 5% 3 3 3 8%	2233
	21st to end	Night	13% 15% 7% 16% 14% 4 5% 4 3 4 16%	1776
March	1st to 10th	Night	17% 14% 7% 13% 11% 4 4 3 4 5% 17%	2151
	11th to 20th	Night	16% 15% 6% 13% 9% 5% 5% 6% 4 4 17%	2101
	21st to end	Night	19% 15% 6% 10% 8% 5% 5% 4 4 5% 19%	1980
April	1st to 10th	Night	24% 17% 8% 11% 5% 2 4 3 4 5% 16%	1800
	11th to 20th	Night	19% 15% 6% 8% 6% 3 4 3 4 6% 27%	1749
	21st to end	Night	20% 13% 6% 7% 5% 3 4 4 4 6% 27%	1564
May	1st to 10th	Night	27% 10% 3 6% 4 3 4 4 5% 6% 29%	1440
	11th to 20th	Night	26% 10% 3 5% 4 2 3 4 4 6% 33%	1416
	21st to end	Night	29% 7% 3 5% 4 2 4 4 5% 8% 29%	1550
June	1st to 10th	Night	31% 10% 4 7% 5% 2 4 4 4 6% 22%	1296
	11th to 20th	Night	22% 9% 3 5% 4 3 4 5% 6% 7% 32%	1260
	21st to end	Night	28% 9% 4 7% 7% 4 5% 5% 5% 6% 22%	1270
July	1st to 10th	Night	28% 8% 3 7% 5% 3 4 5% 5% 7% 25%	1440
	11th to 20th	Night	22% 8% 5% 6% 5% 3 4 4 5% 8% 29%	1440
	21st to end	Night	30% 9% 4 6% 5% 2 4 4 4 7% 25%	1573
August	1st to 10th	Night	21% 8% 4 6% 7% 3 5% 5% 7% 8% 27%	1433
	11th to 20th	Night	24% 9% 3 5% 6% 3 5% 4 4 6% 30%	1467
	21st to end	Night	23% 8% 3 5% 5% 3 4 5% 5% 7% 32%	1966
September	1st to 10th	Night	27% 7% 3 5% 4 4 5% 4 6% 7% 30%	1800
	11th to 20th	Night	30% 9% 2 4 4 3 3 4 5% 6% 27%	1871
	21st to end	Night	28% 9% 4 6% 5% 3 4 3 4 6% 29%	1980
October	1st to 10th	Night	25% 9% 3 6% 4 3 4 5% 6% 7% 27%	2114
	11th to 20th	Night	30% 12% 4 8% 5% 3 4 3 5% 5% 21%	2245
	21st to end	Night	29% 16% 5% 8% 5% 3 3 3 4 7% 18%	2574
November	1st to 10th	Night	28% 19% 6% 9% 7% 3 4 4 4 4 12%	2408
	11th to 20th	Night	28% 20% 7% 10% 6% 3 3 3 4 4 11%	2650
	21st to end	Night	25% 23% 10% 12% 7% 3 4 3 3 3 8%	2740
December	1st to 10th	Night	23% 23% 10% 15% 8% 3 3 3 2 3 7%	2850
	11th to 20th	Night	33% 19% 9% 16% 8% 3 2 2 2 2 5%	3531
	21st to end	Night	21% 21% 11% 17% 8% 3 3 3 3 3 6%	5061

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	88% 2 5% 4 1	1517
	11th to 20th	Day	88% 2 4 4 1	1520
	21st to end	Day	88% 2 4 5% 1	1593
February	1st to 10th	Day	86% 4 5% 4 1	1485
	11th to 20th	Day	81% 3 7% 7% 2	1621
	21st to end	Day	77% 4 6% 9% 4	1480
March	1st to 10th	Day	72% 4 9% 11% 4	1800
	11th to 20th	Day	74% 3 7% 11% 4	1855
	21st to end	Day	69% 3 7% 13% 5% 2	2376
April	1st to 10th	Day	74% 3 8% 10% 4 1	2160
	11th to 20th	Day	58% 3 11% 19% 9%	2160
	21st to end	Day	61% 3 13% 16% 7% 1	2394
May	1st to 10th	Day	60% 3 12% 16% 9%	2520
	11th to 20th	Day	54% 2 14% 18% 10% 1	2482
	21st to end	Day	59% 4 14% 16% 6%	2724
June	1st to 10th	Day	62% 4 12% 16% 6%	2662
	11th to 20th	Day	50% 6% 17% 22% 5%	2700
	21st to end	Day	62% 4 13% 13% 7%	2684
July	1st to 10th	Day	54% 6% 17% 20% 4	2450
	11th to 20th	Day	55% 4 14% 22% 5%	2444
	21st to end	Day	60% 4 16% 17% 3	2592
August	1st to 10th	Day	54% 5% 20% 18% 3	2492
	11th to 20th	Day	58% 4 16% 15% 5%	2433
	21st to end	Day	55% 3 20% 17% 4	2386
September	1st to 10th	Day	55% 4 15% 18% 8% 1	2160
	11th to 20th	Day	61% 4 13% 16% 4 1	2089
	21st to end	Day	62% 4 14% 14% 5%	1980
October	1st to 10th	Day	58% 4 13% 19% 5% 1	1843
	11th to 20th	Day	66% 3 14% 13% 4	1714
	21st to end	Day	72% 3 10% 10% 3	1782
November	1st to 10th	Day	80% 3 7% 7% 2	1670
	11th to 20th	Day	77% 4 6% 11% 2	1525
	21st to end	Day	82% 5% 7% 4 2	1436
December	1st to 10th	Day	86% 3 5% 5%	1330
	11th to 20th	Day	87% 3 5% 4 1	1667
	21st to end	Day	84% 2 7% 5% 1	2601
January	1st to 10th	Night	88% 3 4 4 1	2649
	11th to 20th	Night	86% 4 5% 4 1	2660
	21st to end	Night	86% 2 4 5% 1	2797
February	1st to 10th	Night	89% 3 4 3 2	2471
	11th to 20th	Night	81% 4 9% 5% 1	2236
	21st to end	Night	74% 2 7% 11% 5%	1776
March	1st to 10th	Night	71% 3 8% 12% 5%	2160
	11th to 20th	Night	70% 4 7% 14% 4	2102
	21st to end	Night	67% 3 11% 11% 7% 1	1980
April	1st to 10th	Night	71% 4 9% 11% 4	1800
	11th to 20th	Night	61% 3 11% 16% 8% 1	1749
	21st to end	Night	59% 4 13% 16% 6%	1564
May	1st to 10th	Night	57% 4 13% 19% 6% 1	1440
	11th to 20th	Night	54% 3 12% 21% 9% 1	1417
	21st to end	Night	56% 5% 13% 20% 7%	1551
June	1st to 10th	Night	65% 4 9% 17% 5%	1296
	11th to 20th	Night	53% 6% 15% 20% 6%	1260
	21st to end	Night	63% 6% 12% 14% 5%	1270
July	1st to 10th	Night	60% 5% 16% 15% 4	1401
	11th to 20th	Night	55% 5% 13% 20% 6%	1392
	21st to end	Night	62% 3 15% 17% 3	1486
August	1st to 10th	Night	56% 6% 18% 18% 2	1422
	11th to 20th	Night	57% 6% 17% 14% 6% 1	1467
	21st to end	Night	52% 5% 18% 20% 5%	1966
September	1st to 10th	Night	55% 4 16% 19% 6%	1800
	11th to 20th	Night	58% 4 15% 15% 7% 1	1871
	21st to end	Night	58% 4 14% 18% 6%	1980
October	1st to 10th	Night	57% 5% 12% 16% 8% 1	2114
	11th to 20th	Night	66% 4 13% 13% 3	2245
	21st to end	Night	68% 4 12% 12% 4	2574
November	1st to 10th	Night	75% 5% 9% 8% 2	2408
	11th to 20th	Night	78% 5% 8% 8% 2	2650
	21st to end	Night	81% 4 7% 6% 2	2740
December	1st to 10th	Night	84% 3 6% 5% 1	2850
	11th to 20th	Night	87% 3 5% 5% 1	3533
	21st to end	Night	85% 2 7% 5% 1	5061

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	28% 27% 29% 12% 3 1	370
	11th to 20th	Day	31% 22% 27% 15% 4 1	370
	21st to end	Day	27% 21% 29% 19% 4 1	378
February	1st to 10th	Day	33% 26% 27% 10% 4	340
	11th to 20th	Day	30% 24% 29% 12% 5% 1	336
	21st to end	Day	25% 22% 32% 13% 6% 3	280
March	1st to 10th	Day	23% 22% 33% 16% 4 2	340
	11th to 20th	Day	32% 19% 24% 14% 9% 3	364
	21st to end	Day	31% 19% 26% 15% 7% 2	462
April	1st to 10th	Day	36% 21% 27% 11% 3	420
	11th to 20th	Day	27% 17% 29% 18% 8% 1	438
	21st to end	Day	31% 13% 27% 22% 6% 2	600
May	1st to 10th	Day	35% 13% 23% 20% 6% 3	603
	11th to 20th	Day	28% 12% 24% 22% 11% 3	624
	21st to end	Day	34% 12% 29% 17% 6% 2	680
June	1st to 10th	Day	34% 7% 26% 21% 10% 2	630
	11th to 20th	Day	28% 9% 23% 26% 11% 2	630
	21st to end	Day	34% 11% 23% 20% 10% 3	630
July	1st to 10th	Day	32% 6% 26% 22% 12% 2	620
	11th to 20th	Day	32% 9% 23% 23% 13%	618
	21st to end	Day	34% 8% 23% 22% 12% 1	685
August	1st to 10th	Day	27% 7% 23% 28% 13% 2	625
	11th to 20th	Day	28% 8% 25% 27% 11% 2	617
	21st to end	Day	27% 10% 29% 21% 11% 2	505
September	1st to 10th	Day	26% 13% 29% 24% 6% 2	450
	11th to 20th	Day	36% 14% 29% 15% 6% 1	414
	21st to end	Day	35% 15% 27% 16% 6% 2	360
October	1st to 10th	Day	29% 18% 29% 16% 7% 2	360
	11th to 20th	Day	35% 15% 22% 15% 11% 2	360
	21st to end	Day	39% 18% 18% 19% 6% 1	396
November	1st to 10th	Day	43% 21% 21% 11% 4	365
	11th to 20th	Day	39% 16% 22% 15% 7% 2	370
	21st to end	Day	41% 20% 23% 13% 4	370
December	1st to 10th	Day	38% 19% 25% 12% 6% 1	370
	11th to 20th	Day	37% 22% 27% 12% 1 1	370
	21st to end	Day	30% 23% 23% 16% 7% 1	407
January	1st to 10th	Night	31% 23% 26% 15% 4	850
	11th to 20th	Night	31% 24% 27% 14% 3 1	850
	21st to end	Night	24% 18% 31% 21% 6%	889
February	1st to 10th	Night	29% 22% 28% 17% 3	778
	11th to 20th	Night	27% 22% 31% 15% 4 1	703
	21st to end	Night	22% 16% 30% 20% 10% 3	592
March	1st to 10th	Night	23% 23% 30% 18% 5% 1	720
	11th to 20th	Night	24% 17% 24% 26% 8% 1	716
	21st to end	Night	28% 13% 28% 22% 8% 1	594
April	1st to 10th	Night	36% 13% 27% 18% 6%	540
	11th to 20th	Night	26% 14% 24% 28% 8% 1	534
	21st to end	Night	27% 12% 24% 28% 8% 1	540
May	1st to 10th	Night	31% 7% 20% 30% 10% 2	540
	11th to 20th	Night	31% 6% 20% 29% 13% 2	532
	21st to end	Night	32% 8% 21% 30% 8% 1	583
June	1st to 10th	Night	36% 5% 20% 28% 10% 1	540
	11th to 20th	Night	25% 7% 19% 35% 13% 1	540
	21st to end	Night	30% 6% 20% 29% 13% 1	540
July	1st to 10th	Night	32% 7% 18% 28% 14% 1	526
	11th to 20th	Night	27% 6% 19% 35% 13%	522
	21st to end	Night	34% 5% 14% 33% 13% 1	590
August	1st to 10th	Night	26% 6% 15% 37% 16% 1	538
	11th to 20th	Night	29% 6% 20% 30% 13% 1	532
	21st to end	Night	27% 6% 20% 30% 15% 1	594
September	1st to 10th	Night	28% 10% 22% 29% 10% 1	540
	11th to 20th	Night	35% 8% 23% 28% 7%	540
	21st to end	Night	31% 11% 30% 21% 7% 1	540
October	1st to 10th	Night	30% 11% 26% 27% 6%	674
	11th to 20th	Night	37% 12% 17% 25% 8% 1	762
	21st to end	Night	37% 15% 22% 20% 5%	891
November	1st to 10th	Night	39% 18% 22% 17% 4	830
	11th to 20th	Night	40% 12% 24% 17% 6% 1	850
	21st to end	Night	40% 18% 23% 17% 3	850
December	1st to 10th	Night	34% 21% 22% 17% 6%	850
	11th to 20th	Night	35% 23% 26% 14% 2	850
	21st to end	Night	27% 21% 27% 17% 5% 1	935

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